The present invention relates to an electrical fly-by-wire system for operating an aircraft rudder.
It is known that, at the present time, in most aircraft, a rudder is operated via a mechanical link positioned between the rudder bar, actuated by the pilot, and the rudder. However, electrical fly-by-wire operation of such a rudder has already been envisaged, in the image of what is already done with the other control surfaces, the flaps, ailerons, spoilers, etc.
Furthermore, it is known that such a rudder is engineered on the basis of calculated loadings applied to the aircraft during standardized maneuvers. In roll and yaw, these maneuvers consist in influencing the rudder by sharp actions on the rudder bar, up to the point where the rudder has reached its full travel.
A subject of the present invention is an electrical fly-by-wire system for operating a rudder, by virtue of which it is possible to limit the lateral loadings applied during maneuvers to the rudder and therefore reduce the size and mass thereof, without thereby reducing the flyability of the aircraft or flight safety.
To this end, according to the invention, the electrical fly-by-wire system for operating an aircraft rudder, the rudder being mounted so that it can rotate about an axis so that it can adopt any angular position whatsoever within a range of travel extending on each side of the neutral position of the rudder and limited on each side of this neutral position by a maximum travel value, and the system including:
a rudder bar actuated by the pilot and associated with a transducer that delivers an electrical control command that represents the action of the pilot on the rudder bar; and
an actuator receiving an operating command derived from the control command and moving the rudder about the axis.
The system is notable in that:
between the rudder bar and the actuator there are filters of the low-pass type receiving the control command from the transducer and generating the operating command for the actuator; and
the higher the fraction of the maximum travel value to which the amplitude of the control command corresponds, the higher the time constant of the filter.
Thus, by virtue of the present invention, non-linear filtering which depends on the travel available to the rudder is introduced into the control commands at the rudder bar, this filtering being all the greater the nearer the rudder gets to the end stops delimiting maximum travel, thus limiting the loadings applied to the rudder and therefore making it possible for its size and mass to be reduced.
Furthermore, it is known that it is customary for an operating system of the type recalled hereinabove to include, in addition, a yaw-stabilizer that generates a stabilizing command which is added to the control command at the rudder bar. In this case, the level of the maximum loadings on the rudder becomes particularly critical when these commands are of the same sign.
Hence, according to another particular feature of the present invention, the operating system additionally includes a yaw-stabilizer that stabilizes the aircraft in terms of yaw, generating a yaw-stabilizing command, and a first adder that sums the yaw-stabilizing command and the actuator operating command. Also, a sign identifier is provided, which is capable of determining whether the control command and the yaw-stabilizing command are of the same sign or of opposite signs. The sign identifier acts on the filters to increase their time constant when the control command and the stabilizing command are of the same sign.
Thus, the loadings applied to the rudder are reduced even more by further filtering of the control command at the rudder bar when the rudder is close to its position of maximum travel and when this command and the yaw-stabilizing command are of the same sign.
In a practical embodiment, the system according to the present invention includes:
a limiter receiving the control command and delivering an output signal which is:
either the control command, when the amplitude thereof corresponds to a travel value below a limit equal to a predetermined fraction of the maximum travel value;
or a limit value corresponding to the limit when the amplitude of the control command is greater than this limit value;
a first low-pass filter having a first time constant and receiving the output signal from the limiter;
a subtractor calculating the difference between the control command and the output signal from the limiter;
a second low-pass filter having a second time constant higher than the first time constant and receiving the difference calculated by the subtractor; and
a second adder summing the output signals from the first and second filters, so as to generate a filtered control command for the actuator.
When this system is provided with the aforementioned yaw-stabilizer, it may additionally include:
a third low-pass filter having a third time constant higher than the second time constant and receiving the difference calculated by the subtractor;
a controlled switch inserted between the second and third low-pass filters, on the one hand, and the second adder, on the other hand, so as to be able to send to the second adder, either the output signal from the second low-pass filter or the output signal from the third low-pass filter; and
a switch controller that:
connects the second low-pass filter to the second adder when the yaw-stabilizing command and the electrical control command are of opposite signs; or
connects the third low-pass filter to the second adder when the yaw-stabilizing command and the electrical control command are of the same sign.
Preferably, the first, second and third low-pass filters are of the first-order type, with a transfer function of the form       1          1      +              τ        ⁢                  xe2x80x83                ⁢        p              ,
xcfx84 being the respective time constant xcfx841, xcfx842 or xcfx843 of the first, second and third filters and p being the LAPLACE variable.
The first (xcfx841), second (xcfx842) and third (xcfx843) time constants may have respective values of between 100 ms and 500 ms; 500 ms and 1 second; and 1 second and 2 seconds.
Furthermore, the limit may correspond to roughly 70% of the maximum value of travel of the rudder.